A semi-automatic, or self-loadingfirearm is a gun that requires only a trigger pull for each round that is fired, unlike a single-action revolver, a pump-action firearm, a bolt-action firearm, or a lever-action firearm, which require the shooter to manually chamber each successive round. Also, unlike a double-action revolver, power from one shot is used load the next, instead of using power from pulling the trigger.